Lecture 4- Mitosis and the Eukaryotic Cell September 21/2016
Chromosome segregation: Equal distribution of daughter chromosomes to each of the two cells that
result from cell division.
1. Phases and main characteristics of the cell cycle.
➢ G0 phase- many cells stop dividing.
➢ G1- cell carries out its function; makes RNA, proteins, molecules; growth.
➢ S phase- DNA replication and chromosome duplication occur; continues synthesis.
➢ G2- Gap in cell cycle where growth continues; cell prepares for mitosis and cytokinesis;
Continues to synthesize RNA, proteins, etc.; continues to grow; end signals mitosis.
*No DNA synthesis during G1 and G2
Mitosis is the shortest phase.
2. Stages of Mitosis and Changes in Amount of DNA
Human chromosomes are diploid (2n=46; 23 pairs)
Diploid means 2n, 23 pairs, 46 chromosomes. Halpoid is n.
- Chromosomes begin to condense; appear as thing threads
- 23 pairs of chromosomes
- Mitotic spindle begins to form
- Nuclear envelope breaks down at the end
- Spindle microtubules grow from centrosomes towards centre and grab onto
- Chromosome made up of two sister chromatids held together at centromeres
- Kinetochore- consists of proteins; attached to centromere; mediates attachment and
movement of chromosomes along mitotic spindle.
- Kinetochore microtubules bind to the kinetochores. Attach sister chromatids to
microtubules. Determines outcome of mitosis
- Spindle fibres move chromosomes